Nitrogen PSA Unit

Rated Capacity: 2 to 15 MMSCFD

Images of PSA Unit for sale.

$2,750,000.00 USD

TERMS: $1,250,000.00 down
Monthly Payments of $50,000.00 until brought on-line
Balance payable at $100,000.00 per month for one year at 8% interest
with balloon in first month of 2nd year

Pressure Swing Adsorption Basic Principles

The basic principles of the PSA separation process are explained in this section. The choice of a suitable operating cycle is critical to the operation of the process.

Elementary Steps

Any PSA cycle can be considered as a sequence of elementary steps, the most common of which are as follows (the processes may differ slightly in the sequence of the elementary steps that are utilized):

• Pressurization with the feed gas stream
• High pressure feed from the gas supply
• Depressurization or blow-down removing the waste product
• Desorption at the lower operating pressure, which may be accomplished by evacuation
• Pressure equalization prior to the blow-down step to conserve energy
• Rinsing or purging with the preferential adsorbed gas at high pressure following the adsorption step

Gas phase procedures generally consist of the adsorption column undergoing (in sequence) pressurization, high pressure adsorption, blow-down and low pressure desorption to remove the product gas. The most commonly used system was developed from the Skarstrom cycle utilizing two or more packed adsorbent beds and using four steps to comprise the cycle consisting of pressurization, adsorption, counter current blow-down, and counter current purge. All the beds undergo these four operations and the sequence is phased in a way that a continuous flow product is maintained.

In the first step of a two-bed system, for instance, bed number two would be pressurized to higher operating pressure with feed from the feed gas while bed one is blown down to the atmospheric pressure in the opposite direction. In the second step, high pressure feed flows through bed two. The more strongly adsorbed component is retained in the bed, which in this case would be the hydrocarbon and a gas stream with the less strongly adsorbed component being the nitrogen would leave as the waste gas at a pressure only slightly below that of the feed gas. In order to remove the product gas from the carbon bed, bed one is then purged by further reducing the pressure to atmosphere. At that time bed one is then ready to be refilled from feed gas allowing the activated carbon to adsorb the hydrocarbons prior to ejecting the nitrogen.

Vacuum Swing Cycle

The activated carbon nitrogen removal Pressure Swing Adsorption System is really a Skarstrom cycle in which a vacuum replaces the low-pressure counter current product purge step of desorption. The product end of the column is kept closed and the vacuum is pulled through the feed end to remove the product. Two or more columns are utilized in the sequence, which would be on column one vacuum, repressurization, feed and product removal, and blow-down. At the same time, column two would be receiving feed discharging product followed by blow-down, vacuum and repressurization. The nitrogen rejection PSA system normally is operated at a pressure of 50 pounds then reducing to atmosphere in the vacuum cycle.

Nitrogen Rejection Using Pressure Swing Adsorption

Pressure Swing Adsorption (PSA) is not a new process. Since the 1990's it has been used with widespread commercial acceptance as an acceptable, if not the technology of choice for several specific applications including separation of nitrogen from methane. Pressure Swing Adsorption preocesses are used for many other puposes including separation of carbon dioxide from methane, hydrogen recover, helium recovery, and other related applications.

The principle of Pressure Swing Adsorption is based on using an adsorbent material that preferentially adsorbs one component from a mixed feed. The selectivity may depend on a diference in adsorption equilibrium or in sorption rates, which would be a form of kinetic energy.

All adsorption separation processes involve two principle steps and those steps are adsorption during which the preferenctially adsorbed species are picked up from the feed and the regeneration or desorption process during which the species are removed from the adsorbent thus regenerating the adsorbent for use in the next cycle. Depending on the feed gas composition and the components in the feed gas, it is possible to obtain useful products from either the adsorption or the regeneration or desorption step of the process. The generally accepted princple of a Pressure Swing Adsorption process is that during the regeneration phase the preferentially adsorbed species are removed by reducing the total pressure rather than by utilizing a temperature purge for displacing the product material.

The process of nitrogen rejection from hydrocarbons is normally done by adsorbing the hydrocarbon in a carbon bed. This allows the nitrogen to be purged off from the system. Reducing the pressure in the bed to desorb the hydrocarbons that it now contains then regenerates the carbon bed. The feed step is normally terminated before the more strongly adsorbed component breaks through the bed. The regeneration step is generally terminated before the bed is fully desorbed.

One of the major advantages of using Pressure Swing Adsorption, relative to other types of adsorption processes such as temperature or thermal swing, is that the pressure can be changed very rapidly in the bed. With a temperature differential, it takes a substantial period of time to make adequate temperature changes in that process.

It is important in properly using a PSA process, that the components not be too strongly adsorbed. This allows the preferentially adsorbed product to be used without an uneconomical high vacuum during the regeneration step. The primary difference with a PSA process from other conventional separation processes is that the process operates under transient conditions, unlike other processes such as adsorption extraction or distillation, which will operate under steady state conditions.

One of the primary advantages of Pressure Swing Adsorption over cryogenic processes, is that the Pressure Swing Adsorption process can be brought to operating conditions very quickly. In a cryogenic process a substantial cool down time is required prolonging the treatment process.

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